Communication system

ABSTRACT

In a communication system, a plurality of base stations includes an MeNB being a first base station, and a plurality of SeNBs to be connected to the MeNB. At least one of control plane data about control of communication and user plane data about a user is transmitted to and received from a user equipment (UE) via the first base station being the MeNB. The control plane data and the user plane data are contained in information provided by a core network about communication with the UE. The communication system can simplify processing of at least one of control plane data and user plane data when a communication terminal device communicates with a plurality of base station devices.

TECHNICAL FIELD

The present invention relates to a communication system in which radiocommunication is performed between a communication terminal device suchas a user equipment device and a base station device.

BACKGROUND ART

The 3rd generation partnership project (3GPP), the standard organizationregarding the mobile communication system, is studying communicationsystems referred to as long term evolution (LTE) regarding radiosections and system architecture evolution (SAE) regarding the overallsystem configuration including a core network and a radio accessnetwork, which will be hereinafter collectively referred to as a networkas well (for example, see Non-Patent Documents 1 to 8). Thiscommunication system is also referred to as 3.9 generation (3.9 G)system.

As the access scheme of the LTE, orthogonal frequency divisionmultiplexing (OFDM) is used in a downlink direction and single carrierfrequency division multiple access (SC-FDMA) is used in an uplinkdirection. Further, differently from the wideband code division multipleaccess (W-CDMA), circuit switching is not provided but a packetcommunication system is only provided in the LTE.

The decisions by 3GPP regarding the frame configuration in the L 1Esystem described in Non-Patent Document 1 (Chapter 5) will be describedwith reference to FIG. 1. FIG. 1 is a diagram illustrating theconfiguration of a radio frame used in the LTE communication system.With reference to FIG. 1, one radio frame is 10 ms. The radio frame isdivided into ten equally sized subframes. The subframe is divided intotwo equally sized slots. The first and sixth subframes contain adownlink synchronization signal per radio frame. The synchronizationsignals are classified into a primary synchronization signal (P-SS) anda secondary synchronization signal (S-SS).

Non-Patent Document 1 (Chapter 5) describes the decisions by 3GPPregarding the channel configuration in the LTE system. It is assumedthat the same channel configuration is used in a closed subscriber group(CSG) cell as that of a non-CSG cell.

A physical broadcast channel (PBCH) is a channel for downlinktransmission from a base station device (hereinafter may be simplyreferred to as a “base station”) to a communication terminal device(hereinafter may be simply referred to as a “communication terminal”)such as a user equipment device (hereinafter may be simply referred toas a “user equipment”). A BCH transport block is mapped to foursubframes within a 40 ms interval. There is no explicit signalingindicating 40 ms timing.

A physical control format indicator channel (PCFICH) is a channel fordownlink transmission from a base station to a communication terminal.The PCFICH notifies the number of orthogonal frequency divisionmultiplexing (OFDM) symbols used for PDCCHs from the base station to thecommunication terminal. The PCFICH is transmitted per subframe.

A physical downlink control channel (PDCCH) is a channel for downlinktransmission from a base station to a communication terminal. The PDCCHnotifies of the resource allocation information for downlink sharedchannel (DL-SCH) being one of the transport channels described below,resource allocation information for a paging channel (PCH) being one ofthe transport channels described below and hybrid automatic repeatrequest (HARM) information related to DL-SCH. The PDCCH carries anuplink scheduling grant. The PDCCH carries acknowledgement(Ack)/negative acknowledgement (Nack) that is a response signal touplink transmission. The PDCCH is referred to as an L1/L2 control signalas well.

A physical downlink shared channel (PDSCH) is a channel for downlinktransmission from a base station to a communication terminal. A downlinkshared channel (DL-SCH) that is a transport channel and a PCH that is atransport channel are mapped to the PDSCH.

A physical multicast channel (PMCH) is a channel for downlinktransmission from a base station to a communication terminal. Amulticast channel (MCH) that is a transport channel is mapped to thePMCH.

A physical uplink control channel (PUCCH) is a channel for uplinktransmission from a communication terminal to a base station. The PUCCHcarries Ack/Nack that is a response signal to downlink transmission. ThePUCCH carries a channel quality indicator (CQI) report. The CQI isquality information indicating the quality of received data or channelquality. In addition, the PUCCH carries a scheduling request (SR).

A physical uplink shared channel (PUSCH) is a channel for uplinktransmission from a communication terminal to a base station. An uplinkshared channel (UL-SCH) that is one of the transport channels is mappedto the PUSCH.

A physical hybrid ARQ indicator channel (PHICH) is a channel fordownlink transmission from a base station to a communication terminal.The PHICH carries Ack/Nack that is a response signal to uplinktransmission. A physical random access channel (PRACH) is a channel foruplink transmission from the communication terminal to the base station.The PRACH carries a random access preamble.

A downlink reference signal (RS) is a known symbol in the LTEcommunication system. The following five types of downlink referencesignals are defined: a cell-specific reference signal (CRS), an MBSFNreference signal, a data demodulation reference signal (DM-RS) being aUE-specific reference signal, a positioning reference signal (PRS), anda channel state information reference signal (CSI-RS). The physicallayer measurement objects of a communication terminal include referencesignal received power (RSRP).

The transport channels described in Non-Patent Document 1 (Chapter 5)will be described. A broadcast channel (BCH) among the downlinktransport channels is broadcast to the entire coverage of a base station(cell). The BCH is mapped to the physical broadcast channel (PBCH).

Retransmission control according to a hybrid ARQ (HARQ) is applied to adownlink shared channel (DL-SCH). The DL-SCH can be broadcast to theentire coverage of the base station (cell). The DL-SCH supports dynamicor semi-static resource allocation. The semi-static resource allocationis also referred to as persistent scheduling. The DL-SCH supportsdiscontinuous reception (DRX) of a communication terminal for enablingthe communication terminal to save power. The DL-SCH is mapped to thephysical downlink shared channel (PDSCH).

The paging channel (PCH) supports DRX of the communication terminal forenabling the communication terminal to save power. The PCH is requiredto be broadcast to the entire coverage of the base station (cell). ThePCH is mapped to physical resources such as the physical downlink sharedchannel (PDSCH) that can be used dynamically for traffic.

The multicast channel (MCH) is used for broadcast to the entire coverageof the base station (cell). The MCH supports SFN combining of multimediabroadcast multicast service (MBMS) services (MTCH and MCCH) inmulti-cell transmission. The MCH supports semi-static resourceallocation. The MCH is mapped to the PMCH.

Retransmission control according to a hybrid ARQ (HARQ) is applied to anuplink shared channel (UL-SCH) among the uplink transport channels. TheUL-SCH supports dynamic or semi-static resource allocation. The UL-SCHis mapped to the physical uplink shared channel (PUSCH).

A random access channel (RACH) is limited to control information. TheRACH involves a collision risk. The RACH is mapped to the physicalrandom access channel (PRACH).

The HARQ will be described. The HARQ is the technique for improving thecommunication quality of a channel by combination of automatic repeatrequest (ARQ) and error correction (forward error correction). The HARQis advantageous in that error correction functions effectively byretransmission even for a channel whose communication quality changes.In particular, it is also possible to achieve further qualityimprovement in retransmission through combination of the receptionresults of the first transmission and the reception results of theretransmission.

An example of the retransmission method will be described. If thereceiver fails to successfully decode the received data, in other words,if a cyclic redundancy check (CRC) error occurs (CRC=NG), the receivertransmits “Nack” to the transmitter. The transmitter that has received“Hack” retransmits the data. If the receiver successfully decodes thereceived data, in other words, if a CRC error does not occur (CRC=OK),the receiver transmits “AcK” to the transmitter. The transmitter thathas received “Ack” transmits the next data.

The logical channels described in Non-Patent Document 1 (Chapter 6) willbe described. A broadcast control channel (BCCH) is a downlink channelfor broadcast system control information. The BCCH that is a logicalchannel is mapped to the broadcast channel (BCH) or downlink sharedchannel (DL-SCH) that is a transport channel.

A paging control channel (PCCH) is a downlink channel for transmittingpaging information and system information change notifications. The PCCHis used when the network does not know the cell location of acommunication terminal. The PCCH that is a logical channel is mapped tothe paging channel (PCH) that is a transport channel.

A common control channel (CCCH) is a channel for transmission controlinformation between communication terminals and a base station. The CCCHis used in the case where the communication terminals have no RRCconnection with the network. In the downlink direction, the CCCH ismapped to the downlink shared channel (DL-SCH) that is a transportchannel. In the uplink direction, the CCCH is mapped to the uplinkshared channel (UL-SCH) that is a transport channel.

A multicast control channel (MCCH) is a downlink channel forpoint-to-multipoint transmission. The MCCH is used for transmission ofMBMS control information for one or several MTCHs from a network to acommunication terminal. The MCCH is used only by a communicationterminal during reception of the MBMS.

The MCCH is mapped to the multicast channel (MCH) that is a transportchannel A dedicated control channel (DCCH) is a channel that transmitsdedicated control information between a communication terminal and anetwork on a point-to-point basis. The DCCH is used when thecommunication terminal has an RRC connection. The DCCH is mapped to theuplink shared channel (UL-SCH) in uplink and mapped to the downlinkshared channel (DL-SCH) in downlink.

A dedicated traffic channel (DTCH) is a point-to-point communicationchannel for transmission of user information to a dedicatedcommunication terminal. The DTCH exists in uplink as well as downlink.The DTCH is mapped to the uplink shared channel (UL-SCH) in uplink andmapped to the downlink shared channel (DL-SCH) in downlink.

A multicast traffic channel (MTCH) is a downlink channel for trafficdata transmission from a network to a communication terminal. The MTCHis a channel used only by a communication terminal during, reception ofthe MBMS. The MTCH is mapped to the multicast channel (MCH).

CGI represents a cell global identifier. ECGI represents an E-UTRAN cellglobal identifier. A closed subscriber group (CSG) cell is introduced inthe LTE, and the long term evolution advanced (LTE-A) and universalmobile telecommunication system (UMTS) described below.

The closed subscriber group (CSG) cell is a cell in which subscriberswho are allowed use are specified by an operator (hereinafter, alsoreferred to as a “cell for specific subscribers”). The specifiedsubscribers are allowed to access one or more cells of a public landmobile network (PLMN). One or more cells to which the specifiedsubscribers are allowed access are referred to as “CSG cell(s)”. Notethat access is limited in the PLMN.

The CSG cell is part of the PLMN that broadcasts a specific CSG identity(CSG ID) and broadcasts “TRUE” in a CSG indication. The authorizedmembers of the subscriber group who have registered in advance accessthe CSG cells using the CSG ID that is the access permissioninformation.

The CSG ID is broadcast by the CSG cell or cells. A plurality of CSG IDsexist in the LTE communication system. The CSG IDs are used bycommunication terminals (UEs) for making access from CSG-related memberseasier.

The locations of communication terminals are tracked based on an areacomposed of one or more cells. The locations are tracked for enablingtracking the locations of communication terminals and callingcommunication terminals, in other words, incoming calling tocommunication terminals even in an idle.state. An area for trackinglocations of communication terminals is referred to as a tracking area.

3GPP is studying base stations referred to as Home-NodeB (Home-NB; HNB)and Home-eNodeB (Horne-eNB; HeNB). HNB/HeNB is a base station for, forexample, household, corporation, or commercial access service inUTRAN/E-UTRAN. Non-Patent Document 2 discloses three different modes ofthe access to the HeNB and HNB. Specifically, an open access mode, aclosed access mode, and a hybrid access mode are disclosed.

Further, 3GPP is pursuing specifications standard of long term evolutionadvanced (LTE-A) as Release 10 (see Non-Patent Documents 3 and 4). TheLTE-A is based on the LTE radio communication system and is configuredby adding several new techniques to the system.

Carrier aggregation (CA) is studied for the LTE-A system, in which twoor more component carriers (CCs) are aggregated to support widertransmission bandwidths up to 100 MHz. Non-Patent Document 1 describesthe CA.

In the case where CA is configured, a UE has a single RRC connectionwith a network (NW). In RRC connection, one serving cell provides NASmobility information and security input. This cell is referred to as aprimary cell (PCell). In downlink, a carrier corresponding to PCell is adownlink primary component carrier (DL PCC). In uplink, a carriercorresponding to PCell is an uplink primary component carrier (UL PCC).

A secondary cell (SCell) is configured to form a serving cell group witha PCell, in accordance with the UE capability. In downlink, a carriercorresponding to SCell is a downlink secondary component carrier (DLSCC). In uplink, a carrier corresponding to SCell is an uplink secondarycomponent carrier (UL SCC).

A serving cell group of one PCell and one or more SCells is configuredfor one UE.

The new techniques in the LTE-A include the technique of supportingwider bands (wider bandwidth extension) and the coordinated multiplepoint transmission and reception (CoMP) technique. The CoMP studied forLTE-A in 3GPP is described in Non-Patent Document 1.

The traffic flow of a mobile network is on the rise, and thecommunication rate is also increasing. It is expected that thecommunication rate will be further increased when the operations of theLTE and the LTE-A are fully initiated.

Furthermore, 3GPP is studying the use of small eNBs (hereinafter alsoreferred to as “small-scale base station devices”) configuring smallcells to satisfy tremendous traffic in the future. In an exampletechnique under study, etc., a large number of small eNBs will beinstalled to configure a large number of small cells, thus increasingspectral efficiency and communication capacity. The specific techniquesinclude dual connectivity (abbreviated as DC) in which a UE communicateswith two eNBs through connection thereto. Non-Patent Document 1describes the DC.

Among eNBs that perform dual connectivity (DC), one of them may bereferred to as a master eNB (abbreviated as MeNB), and the other may bereferred to as a secondary eNB (abbreviated as SeNB).

For increasingly sophisticated mobile communications, the fifthgeneration (hereinafter also referred to as “5G”) radio access system isstudied, whose service is aimed to be launched in 2020 and afterward.For example, in the Europe, an organization named METIS summarizes therequirements for 5G (see Non-Patent Document 5).

Among the requirements in the 5G radio access system are a systemcapacity 1000 times as high as, a data transmission rate 100 times ashigh as, a data latency one tenth ( 1/10) as low as, and simultaneouslyconnected communication terminals 100 times as many as those in the LTEsystem, to further reduce the power consumption and device cost.

To satisfy such requirements, increasing the transmission capacity ofdata using broadband frequencies, and increasing the transmission rateof data through increase in the spectral efficiency are being studied.To realize these, the techniques enabling the spatial multiplexing suchas the Multiple Input Multiple Output (MIMO) and the beamforming using amulti-element antenna are being studied.

The MIMO is continuously studied also in LTE-A. From Release 13, fulldimension (FD)-MIMO is studied as the extension of the MIMO, which usestwo-dimensional antenna array. Non-Patent Document 7 describes theFD-MIMO.

It is studied that the 5G radio access system will be installedconcurrently with the LTE system in the initial period of the launch ofits service, which is scheduled in 2020. The following configuration isconsidered. Specifically, a base station for the LTE system (hereinaftermay be referred to as an “LTE base station”) and a base station for the5G radio access system (hereinafter may be referred to as a “5G basestation”) are connected using the dual connectivity (DC) configuration,and the LTE base station is used as an MeNB and the 5G base station asan SeNB.

In this configuration, it is considered that the LTE base station, whichhas a larger cell range, processes control plane (C-plane) data, and theLTE base station and the 5G base station process user plane (U-plane)data. Non-Patent Document 8 describes an example of this configuration.

PRIOR ART DOCUMENTS Non-Patent Documents

-   Non-Patent Document 1: 3GPP TS 36.300 V13.0.0-   Non-Patent Document 2: 3GPP S1-083461-   Non-Patent Document 3: 3GPP TR 36.814 V9.0.0-   Non-Patent Document 4: 3GPP TR 36.912 V10.0.0-   Non-Patent Document 5: “Scenarios, requirements and KPIs for 5G    mobile and wireless system”, [online], Apr. 30, 2013,    ICT-317669-METIS/D1.1, [Searched on Jul. 15, 2016], Internet    <https://www.metis2020.com/documents/deliverables/>-   Non-Patent Document 6: 3GPP TS36.211 V13.0.0-   Non-Patent Document 7: 3GPP TR36.897 V13.0.0-   Non-Patent Document 8: 3GPP R2-163702

SUMMARY Problem to be Solved by the Invention

A DC configuration of using an LTE base station as an MeNB and a 5G basestation as an SeNB is considered for a case when the 5G radio accesssystem is introduced and a plurality of 5G base stations are installedin one location. In this case, the LTE base station needs to processpieces of control plane (C-plane) data of the plurality of 5G basestations.

In addition, when the split bearer configuration is employed, in which apacket data convergence protocol (PDCP) is collected in the MeNB, thereis also a problem concerning processing of user plane (U-plane) data asfollows. That is, since the data amount of a 5G base station is large,the load on an LTE base station due to processing is increased when aplurality of 5G base stations as SeNBs are connected to an LTE basestation as an MeNB.

The present invention has an object to provide a communication systemcapable of simplifying processing of at least one of control plane dataand user plane data when a communication terminal device communicateswith a plurality of base station devices.

Means to Solve the Problem

A communication system according to the present invention includes acommunication terminal device, a plurality of base station devices, anda core network. The plurality of base station devices are configured toperform radio communication with the communication terminal device. Thecore network is configured to provide information about thecommunication with the communication terminal device to the plurality ofbase station devices. The plurality of base station devices include amaster base station device configured to perform main processing, and aplurality of secondary base station devices to be connected to themaster base station device. At least one of control plane data aboutcontrol of the communication and user plane data about a user istransmitted to and received from the communication terminal device viathe master base station device. The control plane data and the userplane data are contained in the information provided by the core networkabout the communication with the communication terminal device.

Effects of the Invention

According to the communication system of the present invention, at leastone of control plane data about control of communication and user planedata about a user is transmitted to and received from a communicationterminal device via a master base station device. The control plane dataand the user plane data are contained in information provided by a corenetwork about communication with the communication terminal device. Thisconfiguration simplifies processing of at least one of control planedata and user plane data when the communication terminal devicecommunicates with a plurality of base station devices.

These and other objects, features, aspects and advantages of the presentinvention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating the configuration of a radio frame foruse in an LTE communication system.

FIG. 2 is a block diagram showing the overall configuration of an LTEcommunication system 200 under discussion of 3GPP.

FIG. 3 is a block diagram showing the configuration of a user equipment202 shown in FIG. 2, which is a communication terminal according to thepresent invention.

FIG. 4 is a block diagram showing the configuration of a base station203 shown in FIG. 2, which is a base station according to the presentinvention.

FIG. 5 is a block diagram showing the configuration of an MME accordingto the present invention.

FIG. 6 is a flowchart showing an outline from a cell search to an idlestate operation performed by a communication terminal (UE) in the LTEcommunication system.

FIG. 7 shows the concept of a cell configuration when macro eNBs andsmall eNBs coexist.

FIG. 8 is a diagram showing the configuration of a conventionalcommunication system 10.

FIG. 9 is a diagram showing the configuration of a communication system20 according to a first embodiment of the present invention.

FIG. 10 is a diagram showing one example of frequencies of transmissionand reception waves used by the communication system 20 according to thefirst embodiment of the present invention.

FIG. 11 is a diagram showing one example of transmission and receptionwaveforms used by the communication system 20 according to the firstembodiment of the present invention.

FIG. 12 is a diagram showing one example of frequencies of transmissionand reception waves used in the example shown in FIG. 11.

FIG. 13 is a diagram showing one example of the flow of data in thecommunication system 20 according to the first embodiment of the presentinvention.

FIG. 14 is a diagram showing one example of the flow of data in acommunication system 20A as another example of the communication systemaccording to the first embodiment of the present invention.

FIG. 15 is a diagram showing one example of a sequence of processingbefore the start of communication in the communication system accordingto the first embodiment of the present invention.

FIG. 16 is a diagram showing the configuration of a communication system40 according to a first modification of the first embodiment of thepresent invention.

FIG. 17 is a diagram showing one example of the flow of data in thecommunication system 40 according to the first modification of the firstembodiment of the present invention.

FIG. 18 is a diagram showing one example of a layout of cells in thecommunication system 40 according to the first modification of the firstembodiment of the present invention.

FIG. 19 is a diagram showing one example of a sequence of processingbefore the start of communication in the communication system 40according to the first modification of the first embodiment of thepresent invention.

FIG. 20 is a diagram showing one example of frequencies of transmissionand reception waves used by a communication system according to a secondmodification of the first embodiment of the present invention.

FIG. 21 is a diagram showing one example of frequencies of transmissionand reception waves used by the communication system according to thesecond modification of the first embodiment of the present invention.

FIG. 22 is a diagram showing one example of frequencies of transmissionand reception waves used by the communication system according to thesecond modification of the first embodiment of the present invention.

FIG. 23 is a diagram showing one example of a sequence of processing tochange an executor of an RRC processing function for a second systemfrom a BS #2 to a BS #1.

FIG. 24 is a diagram showing one example of a sequence of processing tochange an executor of the RRC processing function for the second systemfrom the BS #1 to the BS #2.

FIG. 25 is a diagram showing the configuration of a communication system60 according to a second embodiment of the present invention.

FIG. 26 is a diagram showing one example of a sequence of processing toacquire broadcast information in the communication system 60 accordingto the second embodiment of the present invention.

FIG. 27 is a diagram showing one example of a sequence of processing tonotify of broadcast information based on a request of a UE.

FIG. 28 is a diagram showing another example of a sequence of processingto notify of broadcast information based on a request of the UE.

FIG. 29 is a block diagram showing the configuration of a communicationsystem 80 according to a third embodiment of the present invention.

FIG. 30 is a block diagram showing the configuration of a communicationsystem 80A as another example of the communication system according tothe third embodiment of the present invention.

FIG. 31 is a block diagram showing the configuration of a communicationsystem 90 as still another example of the communication system accordingto the third embodiment of the present invention.

FIG. 32 is a diagram showing one example of a sequence of measurementreport processing of a communication system according to a fourthembodiment of the present invention.

DESCRIPTION OF EMBODIMENTS First Embodiment

FIG. 2 is a block diagram showing an overall configuration of an LTEcommunication system 200, which is under discussion of 3GPP. FIG. 2 willbe described. A radio access network is referred to as an evolveduniversal terrestrial radio access network (E-UTRAN) 201. A userequipment device (hereinafter, referred to as a “user equipment (UE)”)202 that is a communication terminal device is capable of radiocommunication with a base station device (hereinafter, referred to as a“base station (E-UTRAN Node B: eNB)”) 203 and transmits and receivessignals through radio communication.

Here, the “communication terminal device” covers not only a userequipment device such as a movable mobile phone terminal device, butalso an unmovable device such as a sensor. In the following description,the “communication terminal device” may be simply referred to as a“communication terminal”.

The E-UTRAN is composed of one or a plurality of base stations 203,provided that a control protocol for the user equipment 202 such as aradio resource control (abbreviated as RRC), and user planes such as apacket data convergence protocol (PDCP), radio link control (RLC),medium access control (MAC), or physical layer (PHY) are terminated inthe base station 203.

The control protocol radio resource control (RRC) between the userequipment 202 and the base station 203 performs broadcast, paging, RRCconnection management, and the like. The states of the base station 203and the user equipment 202 in RRC are classified into RRC_IDLE andRRC_CONNECTED.

In RRC_IDLE, public land mobile network (PLMN) selection, systeminformation (SI) broadcast, paging, cell re-selection, mobility, and thelike are performed. In RRC_CONNECTED, the user equipment has RRCconnection and is capable of transmitting and receiving data to and froma network. In RRC_CONNECTED, for example, handover (HO) and measurementof a neighbor cell are performed.

The base stations 203 are classified into eNBs 207 and Home-eNBs 206.The communication system 200 includes an eNB group 203-1 including aplurality of eNBs 207 and a Home-eNB group 203-2 including a pluralityof Home-eNBs 206. A system, composed of an evolved packet core (EPC)being a core network and an E-UTRAN 201 being a radio access network, isreferred to as an evolved packet system (EPS). The EPC being a corenetwork and the E-UTRAN 201 being a radio access network may becollectively referred to as a “network”.

The eNB 207 is connected to an MME/S-GW unit (hereinafter, also referredto as an “MME unit”) 204 including a mobility management entity (MME), aserving gateway (S-GW), or an MME and an S-GW by means of an S1interface, and control information is communicated between the eNB 207and the MME unit 204. A plurality of MME units 204 may be connected toone eNB 207. The eNBs 207 are connected to each other by means of an X2interface, and control information is communicated between the eNBs 207.

The Home-eNB 206 is connected to the MME unit 204 by means of an S1interface, and control information is communicated between the Home-eNB206 and the MME unit 204. A plurality of Home-eNBs 206 are connected toone MME unit 204. Or, the Home-eNBs 206 are connected to the MME units204 through a Home-eNB gateway (HeNBGW) 205. The Home-eNB 206 isconnected to the HeNBGW 205 by means of an S1 interface, and the HeNBGW205 is connected to the MME unit 204 by means of an S1 interface.

One or a plurality of Home-eNBs 206 are connected to one HeNBGW 205, andinformation is communicated therebetween through an S1 interface. TheHeNBGW 205 is connected to one or a plurality of MME units 204, andinformation is communicated therebetween through an S1 interface.

The MME units 204 and HeNBGW 205 are entities of higher layer,specifically, higher nodes, and control the connections between the userequipment (UE) 202 and the eNB 207 and the Home-eNB 206 being basestations. The MME units 204 configure an EPC being a core network. Thebase station 203 and the HeNBGW 205 configure the E-UTRAN 201.

Further, 3GPP is studying the configuration below. The X2 interfacebetween the Home-eNBs 206 is supported. In other words, the Home-eNBs206 are connected to each other by means of an X2 interface, and controlinformation is communicated between the Home-eNBs 206. The HeNBGW 205appears to the MME unit 204 as the Home-eNB 206. The HeNBGW 205 appearsto the Home-eNB 206 as the MME unit 204.

The interfaces between the Home-eNBs 206 and the MME units 204 are thesame, which are the S1 interfaces, in both cases where the Home-eNB 206is connected to the MME unit 204 through the HeNBGW 205 and it isdirectly connected to the MME unit 204.

The base station 203 may configure a single cell or a plurality ofcells. Each cell has a range predetermined as a coverage in which thecell can communicate with the user equipment 202 and performs radiocommunication with the user equipment 202 within the coverage. In thecase where one base station 203 configures a plurality of cells, everycell is configured so as to communicate with the user equipment 202.

FIG. 3 is a block diagram showing the configuration of the userequipment 202 of FIG. 2 that is a communication terminal according tothe present invention. The transmission process of the user equipment202 shown in FIG. 3 will be described. First, a transmission data bufferunit 303 stores the control data from a protocol processing unit 301 andthe user data from an application unit 302. The data stored in thetransmission data buffer unit 303 is passed to an encoding unit 304 andis subjected to an encoding process such as error correction. There mayexist the data output from the transmission data buffer unit 303directly to a modulating unit 305 without the encoding process. The dataencoded by the encoding unit 304 is modulated by the modulating unit305. The modulated data is converted into a baseband signal, and thebaseband signal is output to a frequency converting unit 306 and is thenconverted into a radio transmission frequency. After that, atransmission signal is transmitted from an antenna 307 to the basestation 203.

The user equipment 202 executes the reception process as follows. Theradio signal from the base station 203 is received through the antenna307. The received signal is converted from a radio reception frequencyinto a baseband signal by the frequency converting unit 306 and is thendemodulated by a demodulating unit 308. The demodulated data is passedto a decoding unit 309 and is subjected to a decoding process such aserror correction. Among the pieces of decoded data, the control data ispassed to the protocol processing unit 301, and the user data is passedto the application unit 302. A series of processes by the user equipment202 is controlled by a control unit 310. This means that, though notshown in FIG. 3, the control unit 310 is connected to the individualunits 301 to 309.

FIG. 4 is a block diagram showing the configuration of the base station203 of FIG. 2 that is a base station according to the present invention.The transmission process of the base station 203 shown in FIG. 4 will bedescribed. An EPC communication unit 401 performs data transmission andreception between the base station 203 and the EPC (such as the MME unit204), HeNBGW 205, and the like. A communication with another basestation unit 402 performs data transmission and reception to and fromanother base station. The EPC communication unit 401 and thecommunication with another base station unit 402 each transmit andreceive information to and from a protocol processing unit 403. Thecontrol data from the protocol processing unit 403, and the user dataand the control data from the EPC communication unit 401 and thecommunication with another base station unit 402 are stored in atransmission data buffer unit 404.

The data stored in the transmission data buffer unit 404 is passed to anencoding unit 405 and is then subjected to an encoding process such aserror correction. There may exist the data output from the transmissiondata buffer unit 404 directly to a modulating unit 406 without theencoding process. The encoded data is modulated by the modulating unit406. The modulated data is converted into a baseband signal, and thebaseband signal is output to a frequency converting unit 407 and is thenconverted into a radio transmission frequency. After that, atransmission signal is transmitted from an antenna 408 to one or aplurality of user equipments 202.

The reception process of the base station 203 is executed as follows. Aradio signal from one or a plurality of user equipments 202 is receivedthrough the antenna 408. The received signal is converted from a radioreception frequency into a baseband signal by the frequency convertingunit 407, and is then demodulated by a demodulating unit 409. Thedemodulated data is passed to a decoding unit 410 and is then subjectedto a decoding process such as error correction. Among the pieces ofdecoded data, the control data is passed to the protocol processing unit403, the EPC communication unit 401, or the communication with anotherbase station unit 402, and the user data is passed to the EPCcommunication unit 401 and the communication with another base stationunit 402. A series of processes by the base station 203 is controlled bya control unit 411. This means that, though not shown in FIG. 4, thecontrol unit 411 is connected to the individual units 401 to 410.

FIG. 5 is a block diagram showing the configuration of the MME accordingto the present invention. FIG. 5 shows the configuration of an MME 204 aincluded in the MME unit 204 shown in FIG. 2 described above. A PDN GWcommunication unit 501 performs data transmission and reception betweenthe MME 204 a and the PDN GW. A base station communication unit 502performs data transmission and reception between the MME 204 a and thebase station 203 by means of the S1 interface. In the case where thedata received from the PDN GW is user data, the user data is passed fromthe PDN GW communication unit 501 to the base station communication unit502 via a user plane communication unit 503 and is then transmitted toone or a plurality of base stations 203. In the case where the datareceived from the base station 203 is user data, the user data is passedfrom the base station communication unit 502 to the PDN GW communicationunit 501 via the user plane communication unit 503 and is thentransmitted to the PDN GW.

In the case where the data received from the PDN GW is control data, thecontrol data is passed from the PDN GW communication unit 501 to acontrol plane control unit 505. In the case where the data received fromthe base station 203 is control data, the control data is passed fromthe base station communication unit 502 to the control plane controlunit 505.

A HeNBGW communication unit 504 is provided in the case where the HeNBGW205 is provided, which performs data transmission and reception betweenthe MME 204 a and the HeNBGW 205 by means of the interface (IF)according to an information type. The control data received from theHeNBGW communication unit 504 is passed from the HeNBGW communicationunit 504 to the control plane control unit 505. The processing resultsof the control plane control, unit 505 are transmitted to the PDN GW viathe PDN GW communication unit 501. The processing results of the controlplane control unit 505 are transmitted to one or a plurality of basestations 203 by means of the S1 interface via the base stationcommunication unit 502, and are transmitted to one or a plurality ofHeNBGWs 205 via the HeNBGW communication unit 504.

The control plane control unit 505 includes a NAS security unit 505-1,an SAE bearer control unit 505-2, and an idle state mobility managingunit 505-3, and performs an overall process for the control plane. TheNAS security unit 505-1 provides, for example, security of a non-accessstratum (NAS) message. The SAE bearer control unit 505-2 manages, forexample, a system architecture evolution (SAE) bearer. The idle statemobility managing unit 505-3 performs, for example, mobility managementof an idle state (LTE-IDLE state, which is merely referred to as idle aswell), generation and control of a paging signal in the idle state,addition, deletion, update, and search of a tracking area of one or aplurality of user equipments 202 being served thereby, and tracking arealist management.

The MME 204 a distributes a paging signal to one or a plurality of basestations 203. In addition, the MME 204 a performs mobility control of anidle state. When the user equipment is in the idle state and an activestate, the MME 204 a manages a list of tracking areas. The MME 204 abegins a paging protocol by transmitting a paging message to the cellbelonging to a tracking area in which the UE is registered. The idlestate mobility managing unit 505-3 may manage the CSG of the Home-eNBs206 to be connected to the MME 204 a, CSG IDs, and a whitelist.

An example of a cell search method in a mobile communication system willbe described next. FIG. 6 is a flowchart showing an outline from a cellsearch to an idle state operation performed by a communication terminal(UE) in the LTE communication system. When starting a cell search, inStep ST601, the communication terminal synchronizes slot timing andframe timing by a primary synchronization signal (P-SS) and a secondarysynchronization signal (S-SS) transmitted from a neighbor base station.

The P-SS and S-SS are collectively referred to as a synchronizationsignal (SS). Synchronization codes which correspond one-to-one to PCIsassigned per cell, are assigned to the synchronization signals (SSs).The number of PCIs is currently studied in 504 ways. The 504 ways ofPCIs are used for synchronization, and the PC's of the synchronizedcells are detected (specified).

In Step ST602, next, the user equipment detects a cell-specificreference signal (CRS) being a reference signal (RS) transmitted fromthe base station per cell and measures the reference signal receivedpower (RSRP). The codes corresponding one-to-one to the PCIs are usedfor the reference signal RS. Separation from another cell is enabled bycorrelation using the code. The code for RS of the cell is derived fromthe PCI specified in Step ST601, so that the RS can be detected and theRS received power can be measured.

In Step ST603, next, the user equipment selects the cell having the bestRS received quality, for example, the cell having the highest RSreceived power, that is, the best cell, from one or more cells that havebeen detected up to Step ST602.

In Step ST604, next, the user equipment receives the PBCH of the bestcell and obtains the BCCH that is the broadcast information. A masterinformation block (MIB) containing the cell configuration information ismapped to the BCCH over the PBCH. Accordingly, the MIB is obtained byobtaining the BCCH through reception of the PBCH. Examples of the MIBinformation include the downlink (DL) system bandwidth (also referred toas a transmission bandwidth configuration (dl-bandwidth)), the number oftransmission antennas, and a system frame number (SFN).

In Step ST605, next, the user equipment receives the DL-SCH of the cellbased on the cell configuration information of the MIB, to therebyobtain a system information block (SIB) 1 of the broadcast informationBCCH. The SIB1 contains the information about the access to the cell,information about cell selection, and scheduling information on anotherSIB (SIBk; k is an integer equal to or greater than two). In addition,the SIB1 contains a tracking area code (TAC).

In Step ST606, next, the communication terminal compares the TAC of theSIB1 received in Step ST605 with the TAC portion of a tracking areaidentity (TAI) in the tracking area list that has already been possessedby the communication terminal. The tracking area list is also referredto as a TAI list. TAI is the identification information for identifyingtracking areas and is composed of a mobile country code (MCC), a mobilenetwork code (MNC), and a tracking area code (TAC). MCC is a countrycode. MNC is a network code. TAC is the code number of a tracking area.

If the result of the comparison of Step ST606 shows that the TACreceived in Step ST605 is identical to the TAC included in the trackingarea list, the user equipment enters an idle state operation in thecell. If the comparison shows that the TAC received in Step ST605 is notincluded in the tracking area list, the communication terminal requiresa core network (EPC) including MME and the like to change a trackingarea through the cell for performing tracking area update (TAU).

The device configuring a core network (hereinafter, also referred to asa “core-network-side device”) updates the tracking area list based on anidentification number (such as UE-ID) of a communication terminaltransmitted from the communication terminal together with a TAU requestsignal. The core-network-side device transmits the updated tracking arealist to the communication terminal. The communication terminal rewrites(updates) the TAC list of the communication terminal based on thereceived tracking area list. After that, the communication terminalenters the idle state operation in the cell.

Widespread use of smartphones and tablet terminal devices explosivelyincreases traffic in cellular radio communications, causing a fear ofinsufficient radio resources all over the world. To increase spectralefficiency, thus, it is studied to downsize cells for further spatialseparation.

In the conventional configuration of cells, the cell configured by aneNB has a relatively-wide-range coverage. Conventionally, cells areconfigured such that relatively-wide-range coverages of a plurality ofcells configured by a plurality of eNBs cover a certain area.

When cells are downsized, the cell configured by an eNB has anarrow-range coverage compared with the coverage of a cell configured bya conventional eNB. Thus, in order to cover a certain area as in theconventional case, a larger number of downsized eNBs than theconventional eNBs are required.

In the description below, a “macro cell” refers to a cell having arelatively wide coverage, such as a cell configured by a conventionaleNB, and a “macro eNB” refers to an eNB configuring a macro cell. A“small cell” refers to a cell having a relatively narrow coverage, suchas a downsized cell, and a “small eNB” refers to an eNB configuring asmall cell.

The macro eNB may be, for example, a “wide area base station” describedin Non-Patent Document 7.

The small eNB may be, for example, a low power node, local area node, orhotspot. Alternatively, the small eNB may be a pico eNB configuring apico cell, a femto eNB configuring a femto cell, HeNB, remote radio head(RRH), remote radio unit (RRU), remote radio equipment (RRE), or relaynode (RN). Still alternatively, the small eNB may be a “local area basestation” or “home base station” described in Non-Patent Document 7.

FIG. 7 shows the concept of the cell configuration in which macro eNBsand small eNBs coexist. The macro cell configured by a macro eNB has arelatively-wide-range coverage 701. A small cell configured by a smalleNB has a coverage 702 whose range is narrower than that of the coverage701 of a macro eNB (macro cell).

When a plurality of eNBs coexist, the coverage of the cell configured byan eNB may be included in the coverage of the cell configured by anothereNB. In the cell configuration shown in FIG. 7, as indicated by areference “704” or “705”, the coverage 702 of the small cell configuredby a small eNB may be included in the coverage 701 of the macro cellconfigured by a macro eNB.

As indicated by the reference “705”, the coverages 702 of a pluralityof, for example, two small cells may be included in the coverage 701 ofone macro cell. A user equipment (UE) 703 is included in, for example,the coverage 702 of the small cell and performs communication via thesmall cell.

In the cell configuration shown in FIG. 7, as indicated by a reference“706”, the coverage 701 of the macro cell configured by a macro eNB mayoverlap the coverages 702 of the small cells configured by small eNBs ina complicated manner.

As indicated by a reference “707”, the coverage 701 of the macro cellconfigured by a macro eNB may not overlap the coverages 702 of the smallcells configured by small eNBs.

Further, as indicated by a reference “708”, the coverages 702 of a largenumber of small cells configured by a large number of small eNBs may beconfigured in the coverage 701 of one macro cell configured by one macroeNB.

In the fifth generation (5G), which is a forthcoming radio access systemaimed to be commercialized in 2018 to 2020, an architecture ofconcurrently installing an LTE base station for the LTE-A system and a5G base station for the 5G system is considered.

In LTE-A, the configuration of dual connectivity (abbreviated as DC)establishes a master-subordinate relationship of a master eNB (MeNB) anda secondary eNB (SeNB) between two base stations. The MeNB correspondsto a master base station device, and the SeNB corresponds to a secondarybase station device. It is considered that the control plane (C-plane)data is processed solely by the MeNB, and the user plane (U-plane) datais processed by the MeNB and the SeNB.

FIG. 8 is a diagram showing the configuration of a conventionalcommunication system 10. A first base station 11 (hereinafter may bereferred to as a “BS #1”) as an MeNB is connected to a core network 15by means of an S1 interface, and is connected to a second base station12 (hereinafter may be referred to as a “BS #2”) as an SeNB by means ofan Xn interface. A third base station 13 (hereinafter may be referred toas a “BS #3”), which is installed independently of other base stations,is connected to the core network 15 by means of the S1 interface.

In 5G, in addition to LTE-A, a plurality of base stations usingdifferent frequencies are connected. Further, the data amount of eachbase station is also large.

In view of this, a configuration of using LTE-A for the MeNB 11 isconsidered. The reason is that LTE-A can cover a relatively wide cellradius. Specifically, the reason is that LTE-A can cover a cell in arelatively wide range in a plan view due to its use of low frequenciesas well as a large number of already installed base stations presentbecause those base stations are the existing base stations.

A base station of the 5G radio system is allocated to the SeNB 12. Inthis case, it is likely that a base station (hereinafter may be referredto as a “low SHF base station”) that uses low super high frequency (SHF)of frequencies of 6 GHz or lower and a base station (hereinafter may bereferred to as a “high SHF base station”) that uses high SHF offrequencies exceeding 6 GHz are installed concurrently.

In this case, the DC configuration allows only a single SeNB 12, e.g.,only a single low SHF base station, to be allocated to one MeNB 11.Another base station, e.g., a high SHF base station, is only allowed tobe installed as a standalone base station 13 that is independent ofother base stations. That is, a configuration in which a single MeNB 11is connected to a plurality of SeNBs 12 is not possible.

Accordingly, even when a user equipment (hereinafter may be referred toas a “UE”) 14 is capable of concurrently communicating with three ormore base stations, communication paths for pieces of control plane(C-plane) information cannot be integrated into one. Therefore, controlis required such that mismatch between a plurality of pieces of controlplane (C-plane) information does not occur in the UE 14.

Further, even if a plurality of SeNBs 12 are connected, pieces ofcontrol plane (C-plane) information are concentrated at a single MeNB11, which may cause processing capacity of the MeNB 11 to be abottleneck in the network.

The present embodiment has a configuration in which a single basestation corresponding to an MeNB is capable of executing processing ofpieces of control plane (C-plane) data of a plurality of base stationsthat are connected as SeNBs. Further, the present embodiment has aconfiguration in which a single base station corresponding to an MeNB isalso similarly capable of executing processing of pieces of user plane(U-plane) data.

That is, in the present embodiment, control plane (C-plane) data aboutcontrol of communication, which is contained in information provided bythe core network about communication with the UE, is transmitted to andreceived from the UE via a single base station corresponding to an MeNB.This can simplify processing of control plane (C-plane) data performedby a communication terminal capable of concurrently communicating with aplurality of base stations.

FIG. 9 is a diagram showing the configuration of a communication system20 according to a first embodiment of the present invention. Thecommunication system 20 includes a first base station 21 (hereinaftermay be referred to as a “BS #1”), a second base station 22 (hereinaftermay be referred to as a “BS #2”), a third base station 23 (hereinaftermay be referred to as a “BS #3”) and a user equipment (UE) 24. The BS #1is installed as an MeNB. The BS #2 is installed as a first SeNB(hereinafter may be referred to as a “SeNB #1”). The BS #3 is installedas a second SeNB (hereinafter may be referred to as a “SeNB #2”).

The MeNB corresponds to a master base station device. The master basestation device performs main processing. The main processing is, forexample, aggregation processing of the dual connectivity (DC). The firstSeNB and the second SeNB each correspond to a secondary base stationdevice. The first SeNB and the second SeNB are each connected to theMeNB.

A single UE 24 concurrently communicates with the three base stations 21to 23, i.e., the BS #1, the BS #2, and the BS #3. Concerning the threebase stations, for example, the BS #1 is considered to be a base stationof LTE-A, the BS #2 to be a base station of 5G, and the BS #3 to be abase station of 5G. An interface allowing direct communication, i.e., anXn interface in this case, is provided between the BS #1 and the BS #2and also between the BS #1 and the BS #3.

The UE 24 communicates control plane (C-plane) data with the BS #1.Further, the UE 24 communications user plane (U-plane) data with each ofthe BS #1, the BS #2, and the BS #3.

FIG. 10 is a diagram showing one example of frequencies of transmissionand reception waves used by the communication system 20 according to thefirst embodiment of the present invention. In FIG. 10, the horizontalaxis represents frequency f. In the present embodiment, for example, asshown in FIG. 10, the first base station 21 installed as an MeNB, thesecond base station 22 installed as an SeNB #1, and the third basestation 23 installed as an SeNB #2 use transmission and reception wavesof different frequency bands.

FIG. 11 is a diagram showing one example of transmission and receptionwaveforms used by the communication system 20 according to the firstembodiment of the present invention. FIG. 12 is a diagram showing oneexample of frequencies of transmission and reception waves used in theexample shown in FIG. 11. FIG. 11 and FIG. 12 show a case where the basestations 22 and 23 and the UE 24 each use an array antenna as theirtransmission and reception antenna. In this case, as shown in FIG. 11,beam-shaped transmission and reception waveforms 31 to 35 havingdirectivity are used. This configuration can improve spatial separation.

Accordingly, as shown in FIG. 12, a plurality of base stations can beconcurrently allocated to the same frequency band. In the example shownin FIG. 12, one MeNB and two SeNBs use transmission and reception wavesof different frequency bands, while the SeNB #1 and the SeNB #2 usetransmission and reception waves of the same frequency band.

FIG. 13 is a diagram showing one example of the flow of data in thecommunication system 20 according to the first embodiment of the presentinvention. As shown in FIG. 13, for example, user plane (U-plane) datais transmitted and received through communication between a core networkdevice 25 as an upper layer device (a next generation core network) andeach of the base stations, i.e., the first base station 21 (hereinaftermay be referred to as a “BS #1”), the second base station (hereinaftermay be referred to as a “BS #2”), and the third base station(hereinafter may be referred to as a “BS #3”), and is also transmittedand received through communication between each of the base stations andthe UE 24.

The user plane (U-plane) data is not limited thereto, and may betransmitted and received through communication between one base station,e.g., the BS #1, and the core network device 25 as an upper layerdevice, through communication between the BS #1 and the UE 24, andthrough communication between the BS #1 and the UE 24 via the BS #2 orBS #3.

In the present embodiment, control plane (C-plane) data is transmittedand received only through communication between the BS #1 and the UE 24.The communication between the BS #1 and the UE 24 may be performed asdirect communication between the BS #1 and the UE 24, or may beperformed via another base station, such as the BS #3 or the BS #4.

FIG. 14 is a diagram showing one example of the flow of data in acommunication system 20A as another example of the communication systemaccording to the first embodiment of the present invention. Thecommunication system 20A shown in FIG. 14 includes the same componentsas those of the communication system 20 shown in FIG. 13, and thereforethe same components are denoted by the same reference symbols to omitcommon description.

As shown in FIG. 14, control plane (C-plane) data is transmitted andreceived through communication between the core network device 25corresponding to an MME and the BS #1.

The control plane (C-plane) data may be transmitted and received throughcommunication between the BS #1 and the UE 24. Further, as shown in FIG.14, the control plane (C-plane) data may be transmitted and receivedthrough communication with the UE 24 via radio resources of the BS #2and the BS #3, in addition to the communication between the BS #1 andthe UE 24.

FIG. 15 is a diagram showing one example of a sequence of processingbefore the start of communication in the communication system accordingto the first embodiment of the present invention. FIG. 15 shows asequence of adding the BS #2 and the BS #3 in a state where the BS #1and the UE are connected.

In Step ST11, the BS #1, the BS #2, the BS #3, and the UE are connected.

In Step ST12, the BS #1 notifies the BS #2 of a resource allocationrequest. In Step ST13, the BS #2 notifies the BS #1 of a requestacknowledgement.

In Step ST14, the BS #1 notifies the UE of an addition request of the BS#2. In Step ST15, the UE notifies the BS #1 of an addition requestacknowledgement. The UE measures a specified synchronization signal ofthe BS #2.

In Step ST16, the UE synchronizes with a downlink (DL) of the BS #2.

In Step ST17, the BS #2 notifies the UE of channel control, such as aPDCCH.

In Step ST18, the UE starts communication of user plane (U-plane) databased on a resource allocation condition of the downlink signalspecified by the PDCCH.

In Step ST19, the BS #1 notifies the BS #3 of a resource allocationrequest. In Step ST20, the BS #3 notifies the BS #1 of a requestacknowledgement.

In Step ST21, the BS #1 notifies the UE of an addition request of the BS#3. In Step ST22, the UE notifies the BS #1 of an addition requestacknowledgement. The UE measures a specified synchronization signal ofthe BS #3.

In Step ST23, the UE synchronizes with a downlink (DL) of the BS #3.

In Step ST24, the BS #3 notifies the UE of channel control, such as aPDCCH.

In Step ST25, the UE starts communication of user plane (U-plane) databased on a resource allocation condition of the downlink signalspecified by the PDCCH.

Deletion of a base station is executed similarly. Deletion is executedbased on a deletion command of the BS #1 transmitted to the UE.

UEs and base stations compatible with the 5G standard may use an arrayantenna as their transmission and reception antenna. In such a case, theuse of beam-shaped transmission and reception waveforms havingdirectivity can improve spatial separation. Accordingly, a plurality ofbase stations tray be concurrently allocated to the same frequency bandas shown in FIG. 13.

When beams are used, information as to which beam should be selected,such as a beam ID, may be in some cases added to the addition requestsignal of the BS #2 in Step ST14 and to the addition request signal ofthe BS #3 in Step ST21 of FIG. 15. In such a case, a beam for receivingPDCCH can be selected, and thus the PDCCH information need not betransmitted via all of the beams, which can lead to efficient use ofchannel resources.

Alternatively, information as to the selection of a beam can be added tothe PDCCH. In such a case, the BS #1 need not consider beam control.Accordingly, when a plurality of base stations are connected to the BS#1, resource allocation processing of the BS #1 is reduced, and theprocessing load can be distributed as a system. Even if the BS #1 is adevice having limited processing capacity, e.g., an LTE-A base station,processing can be performed while such limited processing capacity isprevented from turning into a bottleneck.

According to the present embodiment as described above, control plane(C-plane) data contained in information provided by the core networkabout communication with the UE is transmitted to and received from theUE via the MeNB. This can simplify processing of control plane (C-plane)data when the UE communicates with a plurality of base stations.

Specifically, in the embodiment, the core network provides control plane(C-plane) data to the MeNB. The MeNB then provides the control plane(C-plane) data provided by the core network to the UE, and to the UEalso via a plurality of SeNBs. This can simplify processing of controlplane (C-plane) data performed by a UE capable of concurrentlycommunicating with a plurality of base stations.

First Modification of First Embodiment

As a first modification of the first embodiment, there is aconfiguration in which part of processing of control plane (C-plane)data is distributed to a base station other than the MeNB, e.g., to a BS#2 described below. FIG. 16 is a diagram showing the configuration of acommunication system 40 according to a first modification of the firstembodiment of the present invention. The communication system 40includes a first base station 41 (hereinafter may be referred to as a“BS #1”), a second base station 42 (hereinafter may be referred to as a“BS #2”), a third base station 43 (hereinafter may be referred to as a“BS #3”), a fourth base station 44 (hereinafter may be referred to as a“BS #4”), a user equipment (UE) 45, and a core network 46.

The present modification shows a case where the BS #1 is a base stationfor LTE-A, and the BS #2, the BS #3, and the BS #4 are each a basestation for 5G. RRC messages for the 5G standard are characterized inbeing transmitted and received collectively by the BS #2.

The BS #1 and the BS #2 are connected by means of an interface betweenbase stations, specifically an Xn interface. Further, the BS #2 and theBS #3 as well as the BS #2 and the BS #4 are connected by means of aninterface between base stations, specifically an Xn interface. The BS #1and the core network 46 are connected by means of an S1 interface.

The BS #1 handles RRC messages for the BS #1, and control plane(C-plane) information for adding the BS #2.

Meanwhile, the BS #2 handles control plane (C-plane) information for theBS #2, the BS #3, and the BS #4. The UE 45 transmits and receives thecontrol plane (C-plane) information to and from the BS #1 and the BS #2.

Adopting the configuration shown in FIG. 16, the BS #1 no longer needsto handle RRC messages of a new system such as 5G. Therefore, even in asystem configuration where a new system such as 5G is connected, a newsystem can be easily introduced.

FIG. 17 is a diagram showing one example of the flow of data in thecommunication system 40 according to the first modification of the firstembodiment of the present invention. FIG. 17 shows an example of alayout of RRC processing functions. The BS #1 employs a first radiosystem (hereinafter may be referred to as a “first system”) of LTE-A,for example. The BS #2, the BS #3, and the BS #4 each employ a secondradio system (hereinafter may be referred to as a “second system”) of5G, for example.

The BS #1 has a function of RRC processing for the first system. The BS#2 has a function of RRC processing for the second system. The RRCmessages for the first system may be transmitted and received betweenthe BS #1 and the UE, or may be communicated to the UE via a radioresource of the BS #2.

Meanwhile, the BS #2 has a function of RRC processing for the secondsystem. RRC messages for the second system may be transmitted andreceived between the BS #2 and the UE, or may be communicated to the UEvia radio resources of the BS #3 and the BS #4. Control plane (C-plane)information for the second system is transmitted and received throughcommunication between the core network 46 and the BS #2. Thecommunication between the core network 46 and the BS #2 may be performedas direct communication between the core network 46 and the BS #2, ormay be performed as communication via the BS #1.

Separating the RRC processing functions for respective radio systems canmaintain independency of each of the radio systems. Therefore, influenceupon other radio systems can be reduced to the extent possible even whena new system is introduced.

Further, connecting a plurality of base stations with associationbetween radio systems as in the dual connectivity can improveconnectivity of a UE, and can smoothly add and delete a cell. The“connectivity of a UE” herein refers to the easiness of connectionbetween a UE and a base station.

FIG. 18 is a diagram showing one example of a layout of cells in thecommunication system 40 according to the first modification of the firstembodiment of the present invention. The connection between the BS #1and the UE can be maintained in a wide range in the case as shown inFIG. 18, for example. That is, the BS #1 forms a macro cell 51 having acell radius of 500 m, for example, the BS #2 forms a micro cell 52having a cell radius of 200 m, for example, and the BS #3 and the BS #4respectively form small cells 53 and 54 each having a cell radius of 50m, for example.

In the example shown in FIG. 18, a BS #2′ as another second base station42A exists in the cell 51 of the BS #1. For example, similarly to the BS#2, the BS #2′ forms a micro cell 52A having a cell radius of 200 m. Inthe cell 52A of the BS #2′, a BS #5 as a fifth base station 45 exists.For example, similarly to the BS #3 and the BS #4, the BS #5 forms asmall cell 55 having a cell radius of 50 m, for example.

Since such a large number of base stations 42, 42A, and 43 to 45 existin the cell 51 of the BS #1, the BS #1 is subjected to a largeprocessing load if intending to process, for all of the base stations42, 42A, and 43 to 45, the pieces of control plane (C-plane) data for aplurality of base stations described in the first embodiment.

In view of this, in the present modification, the BS #2 executesprocessing of control plane (C-plane) data of the BS #2 and processingof control plane (C-plane) data of the BS #3 and the BS #4 that are basestations running under the cell 52 of the BS #2, This configuration canreduce the load on the BS #1 due to the processing. Further, it ispreferable that the BS #2′ also executes processing of control plane(C-plane) data of the BS #2′ and processing of control place (C-plane)data of the BS #5 that is a base station running under the cell 52A ofthe BS #2′. This can further reduce the load on the BS #1 due to theprocessing.

FIG. 19 is a diagram showing one example of a sequence of processingbefore the start of communication in the communication system 40according to the first modification of the first embodiment of thepresent invention. FIG. 19 shows an example of a sequence forestablishing connection with a plurality of base stations. FIG. 19 showsa sequence of adding the BS #2, the BS #3, and the BS #4 in a statewhere the BS #1 and the UE are connected.

In Step ST31, the BS #1 and the UE are connected.

In Step ST32, the BS #1 notifies the BS #2 of a resource allocationrequest. In Step ST33, the BS #2 notifies the BS #1 of a requestacknowledgement.

In Step ST34, the BS #1 notifies the UE of an addition request of the BS#2. In Step ST35, the UE notifies the BS #1 of an addition requestacknowledgement. The UE measures a specified synchronization signal ofthe BS #2.

In Step ST36, the UE synchronizes with a downlink (DL) of the BS #2.

In Step ST37, the BS #2 notifies the UE of channel control, such as aPDCCH.

In Step ST38, the UE starts communication of user plane (U-plane) databased on a resource allocation condition of the downlink signalspecified by the PDCCH.

In Step ST39, the BS #2 notifies the BS #3 of a resource allocationrequest. In Step ST40, the BS #3 notifies the BS #2 of a requestacknowledgement.

In Step ST41, the BS #2 notifies the UE of an addition request of the BS#3.

In Step ST42, the UE notifies the BS #2 of an addition requestacknowledgement. The UE measures a specified synchronization signal ofthe BS #3.

In Step ST43, the UE synchronizes with a downlink (DL) of the BS #3.

In Step ST44, the BS #3 notifies the UE of channel control, such as aPDCCH.

In Step ST45, the UE starts communication of user plane (U-plane) databased on a resource allocation condition of the downlink signalspecified by the PDCCH.

In Step ST46, the BS #2 notifies the BS #4 of a recourse allocationrequest. In Step ST47, the BS #4 notifies the BS #2 of a requestacknowledgement.

In Step ST48, the BS #2 notifies the UE of an addition request of the BS#4.

In Step ST49, the UE notifies the BS #2 of an addition requestacknowledgement. The UE measures a specified synchronization signal ofthe BS #3.

In Step ST50, the UE synchronizes with a downlink (DL) of the BS #4.

In Step ST51, the BS #4 notifies the UE of control channel, such as aPDCCH.

In Step ST52, the UE starts communication of user plane (U-plane) databased on a resource allocation condition of the downlink signalspecified by the PDCCH.

Deletion of a base station is performed similarly to the addition of abase station. Deletion of the BS #2 is performed based on a command fromthe BS #1 to the UE. Further, deletion of the BS #3 and the BS #4 isperformed based on a command of the BS #2.

When the BS #2 is deleted during connection between the BS #3 and the BS#4, the following sequence may be employed. That is, the BS #2 firstissues a deletion command of base stations of the BS #3 and the BS #4,and subsequently the BS #2 is deleted. Alternatively, the BS #1 mayissue a deletion command of the BS #2, allowing the BS #3 and the BS #4to be simultaneously deleted.

When the above-mentioned BS #2 is added, the addition request command ofthe BS #2 that is to be notified of to the UE contains a messageindicating that the BS #2 is valid for the RRC processing function ofthe second system. Further, the request command of resource allocationfrom the BS #1 to the BS #2 contains a message indicating the validityof the RRC processing function. If the message indicates invalidity, theBS #2 is not valid for the RRC processing function of the second system,thus playing the same role as the BS #2 of the first embodiment shown inFIG. 9.

According to the present modification above, the sequence shown in FIG.19 is executed. Specifically, as shown in FIG. 19, radio resourcecontrol (RRC) processing for the BS #2, the BS #3, and the BS #4, eachbeing an SeNB, is performed by one of the BS #2, the BS #3, and the BS#4, e.g., performed by the BS #2. This configuration can reduce the loadon the BS #1 due to the processing of control plane (C-plane) data.Accordingly, a time period taken for sequence processing such asprocessing of adding a base station can be reduced, which in turn canreduce delay of processing.

Second Modification of First Embodiment

As a second modification of the first embodiment, one example is given.Specifically, RRC messages are communicated using a selected CC when aplurality of component carriers (CCs) exist in the BS #2 in theconfiguration of the first modification of the first embodiment shown inFIG. 16. A communication system of the present modification has the sameconfiguration as that of the communication system 40 of the firstmodification of the first embodiment shown in FIG. 16, and thereforeillustration and common description of the configuration are omitted.

FIG. 20 to FIG. 22 are each a diagram showing one example of frequenciesof transmission and reception waves used by a communication systemaccording to a second modification of the first embodiment of thepresent invention. In FIG. 20 to FIG. 22, the horizontal axis representsfrequency f. FIG. 20 shows frequencies of transmission and receptionwaves used by the BS #1. FIG. 21 shows frequencies of transmission andreception waves used by the BS #2. FIG. 22 shows frequencies oftransmission and reception waves used by the BS #3 and the BS #4.

As shown in FIG. 20, the BS #1 uses one type of transmission andreception waves to transmit and receive RRC messages for the firstsystem. A bandwidth BW1 of the transmission and reception waves used bythe BS #1 is 20 MHz, for example.

As shown in FIG. 21, the BS #2 handles two CCs. Therefore, in thepresent modification, RRC messages are transmitted using any of CC #0and CC #1. With this, the UE can obtain necessary RRC informationwithout performing modulation processing and demodulation processing onall of the CCs.

A bandwidth BW2 of the transmission and reception waves used by the BS#2 shown in FIG. 21 is 100 MHz, for example. In the presentmodification, the CC #0, among the two CCs used by the BS #2, is used totransmit and receive RRC messages for the second system.

Further, in the present modification, the CC #1 of the BS #2, to whichRRC is not allocated, is treated equally with other BS #3 and BS #4.This can simplify management of user plane (U-plane) resources.

A bandwidth BW3 of the transmission and reception waves used by the BS#3 shown in FIG. 22 is 100 MHz, for example. When the BS #3 transmitsand receives RRC messages for the second system, the RRC messages aremapped to any CC of CC #0 to CC #7, or to a plurality of CCs. HandlingRRC using only a part of CCs can simplify management of user plane(U-plane) resources of other CCs to which RRC is not mapped.

Third Modification of First Embodiment

As a third modification of the first embodiment, one method is given.Specifically, the configuration of the first embodiment and theconfiguration of the first modification of the first embodiment arecombined. In the first embodiment, the BS #1 executes the RRC processingfunction for the second system. In contrast, in the first modificationof the first embodiment, the BS #2 executes the RRC processing functionfor the second system.

FIG. 23 is a diagram showing one example of a sequence of processing tochange an executor of the RRC processing function for the second systemfrom the BS #2 to the BS #1.

In Step ST61, RRC communication for the second system is performedbetween the BS #2 and the UE.

In Step ST62, the BS #1 notifies the BS #2 of a release command of RRCprocessing for the second system.

In Step ST63, the BS #2 notifies the BS #1 of a positiveacknowledgement.

In Step ST64, the BS #1 notifies the UE of a change command of the RRCprocessing for the second system. The change command of RRC processingfor the second system is a change command of the RRC processing for thesecond system from the BS #2 to the BS #1. Examples of specific commanddetails include changing a radio resource for handling RRC messages forthe second system, and changing a message format.

In Step ST65, RRC communication for the second system is performedbetween the BS #1 and the UE.

FIG. 24 is a diagram showing one example of a sequence of processing tochange an executor of the RRC processing function for the second systemfrom the BS #1 to the BS #2.

In Step ST71, RRC communication for the second system is performedbetween the BS #1 and the UE.

In Step ST72, the BS #1 notifies the BS #2 of an addition command of RRCprocessing for the second system.

In Step ST73, the BS #2 notifies the BS #1 of a positiveacknowledgement.

In Step ST74, the BS #1 notifies the UE of a change command of the RRCprocessing for the second system. The change command of RRC processingfor the second system is a change command of the RRC processing for thesecond system from the BS #1 to the BS #2. Examples of specific commanddetails include changing a radio resource for handling RRC messages forthe second system, and changing a message format.

In Step ST75, RRC communication for the second system is performedbetween the BS #2 and the UE.

Enabling change of a base station and a resource to perform RRCprocessing as described above in turn enables distribution of the loadof the RRC processing in accordance with a communication condition ofthe UE, available functions of the UE, a loaded condition of the basestation, and the number of connected terminals, for example.

Further, when high speed communication with low latency is demanded inaccordance with a communication condition of the UE, the use of the BS#2 also enables execution of the RRC processing for the second systemwith reduced latency.

In contrast, when the UE does not object to latency etc. and is inpower-saving usage such as by decreasing the number of RRC messages, itis also effective to concentrate the RRC processing for the first systemand the RRC processing for the second system at one entity, i.e., the BS#1, where the transmission and reception of the RRC messages areperformed.

Second Embodiment

In 5G, the concept of beam control may be added. Further, the intervalsat which base station are installed are reduced. This may increase thenumber of base stations in one cell. Further, various types of basestations may be installed concurrently. For example, base stations ofultra-reliability and low latency communication (URLLC) and a pluralityof base stations of different frequencies may be installed concurrently.In such a case, information to be broadcast about base stations isincreased. If the information is transmitted by a single macro basestation, there is a problem in increasing the processing of the macrobase station.

In order to solve such a problem, in the present embodiment, broadcastinformation is divided into basic information and additionalinformation. The basic information is transmitted from the BS #1 havinga large cell radius. The additional information is transmitted from BS#2 that is installed inside the cell of the BS #1 and has a cell radiussmaller than that of the BS #1 or equivalent to that of the BS #1.

This configuration can reduce the amount of broadcast informationtransmitted from a single base station to distribute the load. Further,the amount of information to be transmitted is reduced by narrowingdetails of the broadcast information down to information necessary forindividual base stations. As a result, the occupying proportion of thebroadcast information with respect to the entire radio resource can bereduced. Accordingly, the system can be efficient.

FIG. 25 is a diagram showing the configuration of a communication system60 according to a second embodiment of the present invention. Thecommunication system 60 includes a first base station 61 (hereinaftermay be referred to as a “BS #1”), a second base station 62 (hereinaftermay be referred to as a “BS #2”), a third base station 63 (hereinaftermay be referred to as a “BS #3”), a fourth base station 64 (hereinaftermay be referred to as a “BS #4”), and a user equipment (UE) 65.

The BS #1 forms a macro cell 71 having a cell radius of 500 m, forexample. The BS #2 forms a micro cell 72 having a cell radius of 200 m,for example. The BS #3 and the BS #1 respectively form small cells 73and 74 each having a cell radius of 50 in, for example.

For example, if the base stations 61 to 64 are installed as standalonebase stations independently of other base stations, pieces of broadcastinformation BrI #1 to BrI #3 are transmitted from the respective basestations 61 to 64. Although FIG. 25 omits illustration of broadcastinformation transmitted from the fourth base station 64 for the sake ofavoiding complexity and difficulty in understanding the drawing,broadcast information is in actuality also transmitted from the fourthbase station 64.

The present embodiment, however, assumes a configuration in which aplurality of base stations are connected to the UE 65 under the cell ofthe BS #1 described in the first modification of the first embodiment.Although it is possible that the BS #1 transmits configurationinformation of all of the base stations as broadcast information BrI #1in the present configuration, the BS #1 transmits only configurationinformation of the BS #1 and information necessary for initialconnection of the BS #2 as broadcast information BrI #1 in order toefficiently transmit broadcast information. The BS #2 transmits piecesof broadcast information other than the information necessary for theinitial connection of the BS #2 out of the broadcast information for theBS #2, and pieces of broadcast information for the BS #3 and for the BS#4.

In this manner, in the present embodiment, one of the plurality ofSeNBs, specifically the BS #2, at least partially notifies the UE ofpieces of broadcast information for each of SeNBs, i.e., pieces ofbroadcast information for the BS #2, for the BS #3, and for the BS #4.

Adopting the configuration, the BS #1 no longer needs to transmitbroadcast information for all of the base stations running under thecell. Therefore, the amount of the data of the broadcast information BrI#1 of the BS #1 can be reduced. With this, the occupying proportion ofthe broadcast information BrI #1 with respect to the radio resource ofthe BS #1 can be reduced. Further, reducing the transmission cycle ofthe broadcast information BrI #1 of the BS #1 can reduce the period oftime taken for the UE to complete the initial connection to the BS #1.

The BS #2 may directly notify the UE of broadcast information for eachSeNB as shown in FIG. 26 to be described later, or the BS #2 may notifythe UE of broadcast information for each SeNB via another base stationas shown in FIG. 27 and FIG. 28 to be described later.

Examples of pieces of information necessary for the initial connectionof the BS #2 include SIB1 (cell access and cell reselection relatedinfo, scheduling info list), and SIB2 (radio resource configuration thatis common for all UEs) of broadcast information used in LTE-A. Further,information about transmission and reception beams, being additionalinformation, is considered to be also added to a base station for 5G.The additional information corresponds to pieces of broadcastinformation other than the above-mentioned information necessary for theinitial connection of the BS #2.

FIG. 26 is a diagram showing one example of a sequence of processing toacquire broadcast information in the communication system 60 accordingto the second embodiment of the present invention. FIG. 26 shows oneexample of a sequence of processing in which the UE acquires pieces ofbroadcast information for the BS #1, the BS #2, the BS #3, and the BS#4.

In Step ST81, the BS #1 notifies the UE of broadcast information for theBS #1. The UE reads control information for the BS #1 out of thebroadcast information notified of from the BS #1.

In Step ST82, communication is performed between the BS #1 and the UE.

In Step ST83, the BS #1 notifies the UE of basic information ofbroadcast information for the BS #2. When the UE needs to be connectedto the BS #2, the UE reads the basic information of the broadcastinformation for the BS #2 out of the broadcast information of the BS #1,thereby obtaining information to access the BS #2.

In Step ST84, the BS #2 notifies the UE of additional information of thebroadcast information for the BS #2. The UE reads the additionalinformation of the BS #2 out of the broadcast information of the BS #2.

In Step ST85, communication is performed between the BS #2 and the UE.

In Step ST86, the BS #2 notifies the UE of broadcast information for theBS #3 and broadcast information for the BS #4. When the UE needs to beconnected to the BS #3 or the BS #4, the UE reads control informationfor the BS #3 or control information for the BS #4 out of the broadcastinformation notified of from the BS #2.

In Step ST87, communication is performed between the BS #3 and the UE.In Step ST88, communication is performed between the BS #4 and the UE.

FIG. 27 is a diagram showing one example of a sequence of processing tonotify of broadcast information based on a request of the UE. FIG. 27shows an example where the BS #2 acknowledges a broadcast informationrequest of the UE.

In Step ST91, the BS #1 notifies the UE of broadcast information for theBS #1.

In Step ST92, communication is performed between the BS #1 and the UE.

In Step ST93, the BS #1 notifies the UE of basic information ofbroadcast information for the BS #2.

In Step ST94, the BS #2 notifies the UE of additional information of thebroadcast information for the BS #2.

In Step ST95, communication is performed between the BS #2 and the UE.

In Step ST96, the UE notifies the BS #2 of a broadcast informationrequest for the BS #3.

In Step ST97, the BS #2 notifies the UE of radio resource allocationinformation for notifying of broadcast information.

In Step ST98, the BS #2 notifies the UE of broadcast information for theBS #3 with the radio resource.

In Step ST99, communication is performed between the BS #3 and the UE.

Though the processing shown in FIG. 27, the occupying proportion ofbroadcast information with respect to a radio resource can be reduced.Particularly in 5G, base station configuration information is increaseddue to beam control etc., and also base station configurationinformation is increased due to coping with various scenarios such asmassive machine type connection (mMTC) and ultra-reliability and lowlatency communication (URLLC). Accordingly, efficiency can be enhancedby broadcasting only information necessary for initial connection, andthen individually transmitting the remaining information to the UE.

FIG. 28 is a diagram showing another example of a sequence of processingto notify of broadcast information based on a request of the UE. FIG. 28shows a method of notifying of broadcast information requested by the UEby using a radio resource of a base station, which is different from aradio resource of a base station that has received the request.

In Step ST101, the BS #1 and the UE are communicated.

In Step ST102, the BS #2 and the UE are communicated.

In Step ST103, the BS #3 and the UE are communicated.

In Step ST104, the UE notifies the BS #2 of a broadcast informationrequest for the BS #4.

In Step ST105, the BS #2 notifies the BS #3 of a resource securingrequest for broadcast information notification. Specifically, the BS #2notifies of broadcast information by using a radio resource of the BS#3. The BS #2 informs the BS #3 of the size of the broadcastinformation, information about radio resource in use, etc.

In Step ST106, the BS #3 notifies the BS #2 of secured radio informationif the BS #3 succeeded in securing a radio resource.

In Step ST107, the BS #2 notifies the UE of allocation information ofthe broadcast information.

In Step ST108, the BS #3 notifies the UE of broadcast information forthe BS #4.

5G is also considered to have a configuration in which, by using anarray antenna, beams are formed with transmission and reception antennawaveforms so as to enhance directivity of the antenna. Thisconfiguration enables spatial multiplexing. Such use of a beam resourcecapable of enabling spatial multiplexing for broadcast information canfurther reduce the occupying proportion of broadcast information withrespect to a radio resource.

Further, it is preferable to employ a configuration that allows freeselection of a base station that receives a broadcast informationrequest from the UE, and a base station that transmits a broadcastinformation request from the UE. With this, radio resources can beutilized further effectively.

In communication requiring high reliability, it is also effective that aplurality of base stations transmit the same broadcast information, as away to enhance reliability of data.

Further, as in the second modification of the first embodiment, it ispreferable that a radio resource to transmit broadcast information isdetermined per component carrier (CC) also in the present embodiment.This can utilize an idle radio resource, and thus spectral efficiencycan be improved.

Third Embodiment

Regarding processing of user plane (U-plane) data, the standardconfiguration for the split bearer configuration of dual connectivity upto LTE-A is that the packet data convergence protocol (PDCP) function isassigned to a master eNB (MeNB) so that a secondary eNB (SeNB) performsprocessing of layers lower than the RLC.

In such a configuration, ciphering of the PDCP is concentrated at oneentity, and therefore processing can be simplified. In contrast, 5G isconsidered to have a configuration in which a plurality of base stationscommunicate with one UE as in the first embodiment. In this case, sincethe dual connectivity configuration cannot be applied to three and morebase stations, the third and subsequent base stations need to beindependent of other base stations. Accordingly, there is a problem inthat the processing of the PDCP and the like cannot be simplified.

In order to solve the problem, in the present embodiment, pieces of datasplit from the PDCP of the BS #1 are processed in layers of the RLC andthe lower layers of the BS #2 and the BS #3, as a method of processinguser plane (U-plane) data of the first embodiment.

FIG. 29 is a block diagram showing the configuration of a communicationsystem 80 according to a third embodiment of the present invention. Thecommunication system 80 includes a first base station 81 (hereinaftermay be referred to as a “BS #1”), a second base station 82 (hereinaftermay be referred to as a “BS #2”), a third base station 83 (hereinaftermay be referred to as a “BS #3”), a UE 84, and an upper layer device 85.The BS #1 includes a PDCP processing unit, an RLC processing unit, a MACprocessing unit, and a PHY processing unit. The BS #2 and the BS #3 eachinclude an RLC processing unit, a MAC processing unit, and a PHYprocessing unit. The UE 84 includes a PDCP processing unit, an RLCprocessing unit, a MAC processing unit, and a PHY processing unit forthe BS #1, an RLC processing unit, a MAC processing unit, and a PHYprocessing unit for the BS #2, and an RLC processing unit, a MACprocessing unit, and a PHY processing unit for the BS #3. The upperlayer device 85 includes a core network device and a serving gateway(abbreviated as SGW).

The BS #1 and the BS #2, and the BS #1 and the BS #3 each correspond tothe configuration of the option 3C (split bearer) of dual connectivity.

The BS #1 receives user plane (U-plane) data from the upper layer device85. The PDCP processing unit of the BS #1 performs PDCP processing ofrobust header compression (ROHC) and ciphering processing.

The data, to which a PDCP sequence number (SN) is attached, is splitinto pieces to be transmitted to the RLC processing unit of the BS #1,the RLC processing unit of the BS #2, and the RLC processing unit of theBS #3.

The base stations each perform RLC processing. MAC processing, and PHYprocessing on the split piece of data, and then each transmit theprocessed piece of data to the UE 84. The UE 84 performs PHY processing,MAC processing, and RLC processing for each of the base stations on thepieces of data. Subsequently, the UE 84 collects the processed pieces ofdata into one PDCP. For uplink data, the reverse procedures will betaken.

Such a configuration can simplify processing of the UE, such as PDCPciphering, even in a system where the UE is connected to a plurality ofbase stations.

FIG. 30 is a block diagram showing the configuration of a communicationsystem 80A as another example of the communication system according tothe third embodiment of the present invention. The communication system80A shown in FIG. 30 includes the same components as those of thecommunication system 80 shown in FIG. 29, and therefore the samecomponents are denoted by the same reference symbols to omit commondescription.

The communication system 80A includes a second base station 82A, insteadof the second base station 82 shown in FIG. 29. The second base station82A further includes a data split processing unit (also referred to as a“SPLIT processing unit”) in addition to the components of the secondbase station 82 of FIG. 29.

As shown in FIG. 30, the data split processing unit of the BS #2 allowsa configuration in which the BS #2 transfers, to the BS #3, PDCP datafrom the BS #1. In this configuration, it is sufficient that the BS #1supports a user plane (U-plane) interface that is only compatible withconnection between the BS #1 and the BS #2. Accordingly, thespecifications of the option 3C of dual connectivity of LTE can besupported without making changes thereto.

According to the present embodiment as described above, user plane(U-plane) data, which is contained in information provided by the corenetwork about communication with the UE, is transmitted to and receivedfrom the UE via a single base station BS #1 corresponding to an MeNB.Specifically, the core network provides user plane (U-plane) data to anMeNB. The MeNB then provides the user plane (U-plane) data to the UE,and to the UE also via a plurality of SeNBs. This can simplifyprocessing of user plane (U-plane) data when a UE communicates with aplurality of base stations.

FIG. 31 is a block diagram showing the configuration of a communicationsystem 90 as still another example of the communication system accordingto the third embodiment of the present invention. The communicationsystem 90 includes a first base station 91 (hereinafter may be referredto as a “BS #1”), a second base station 92 (hereinafter may be referredto as a “BS #2”), a third base station 93 (hereinafter may be referredto as a “BS #3”), a fourth base station 94 (hereinafter may be referredto as a “BS #4”), a UE 95, a first core network 96, and a second corenetwork 97. The first core network 96 is a core network for LTE-A. Thesecond core network 97 is a core network for 5G.

The BS #1 and the BS #2 each include a PDCP processing unit, an RLCprocessing unit, a MAC processing unit, and a PHY processing unit. TheBS #3 and the BS #4 each include an RLC processing unit, a MACprocessing unit, and a PHY processing unit. The UE 95 includes a PDCPprocessing unit, an RLC processing unit, a MAC processing unit, and aPHY processing unit for the BS #1, a PDCP processing unit, an RLCprocessing unit, a MAC processing unit, and a PHY processing unit forthe BS #2, an RLC processing unit, a MAC processing unit, and a PHYprocessing unit for the BS #3, and an RLC processing unit, a MACprocessing unit, and a PHY processing unit for the BS #4.

FIG. 31 shows the following configuration as a method of processing userplane (U-plane) data of the first modification of the first embodiment.That is, the BS #1 of LTE-A is connected to a core network for LTE, forexample, the BS #2 of 5G is connected to a core network for 5G, forexample, and the BS #3 and the BS #4 of 5G process pieces of user plane(U-plane) data split from the PDCP processing unit of the BS #2, forexample.

This is one example of a configuration where the BS #1 is a base stationfor LTE-A, and the BS #2, the BS #3, and the BS #4 are each of a basestation for 5G.

The function of the PDCP processing unit for LTE-A and that for 5G maybe different. Even if the function of the PDCP processing unit for LTE-Aand that for 5G are the same, the data amount of user plane (U-plane)data for 5G may be several tens of times larger than the data amount ofuser plane (U-plane) data for LTE, and thus performance of the PDCPprocessing unit of a conventional base station of LTE-A may be abottleneck. In such a case, the PDCP processing for 5G needs to beexecuted by a base station for 5G.

In order to solve the problem as above, the example shown in FIG. 31employs a configuration in which the BS #2 executes PDCP processing ofuser plane (U-plane) data of the 5G system, and the user plane (U-plane)data is then transmitted to the RLC processing units of the BS #3 andthe BS #4 that run under the BS #2.

The BS #1 is connected to the first core network 96 being a core networkfor LTE-A. The BS #1 processes user plane (U-plane) data received fromthe first core network 96 in the PDCP processing unit, the RLCprocessing unit, the MAC processing unit, and the PHY processing unit ofthe BS #1, and then transmits the processed data to the UE 95.

The BS #2 is connected to the second core network 97 being a corenetwork (a next generation core network) for 5G. The BS #2 performsprocessing, such as ROHC, ciphering, and attaching a sequence number(SN) of PDCP, on user plane (U-plane) data received from the second corenetwork 97 in the PDCP processing unit of the BS #2.

The data subjected to the PDCP processing is split into pieces to betransmitted to the RLC processing unit of the BS #2, the RLC processingunit of the BS #3, and the RLC processing unit of the BS #4. The basestations each perform processing on the split piece of data in the RLCprocessing unit, the MAC processing unit, and the PHY processing unit,and then each transmit the processed piece of data to the UE 95.

The UE 95 performs PHY processing, MAC processing, and RLC processingfor each of the base stations on the pieces of data. Subsequently, theUE 95 collects the processed pieces of data into two PDCPs, i.e., a PDCPfor LTE-A and a PDCP for 5G.

This configuration can simplify PDCP processing irrespective ofprocessing capacity of an LTE-A base station. Further, data of 5G can betransmitted and received without a problem even in a case where aconnection interface between the BS #1 and the BS #2 employs a so-called“non ideal network,” which is a network that does not guaranteeprovisions of latency in data processing.

In the example shown in FIG. 31 as above, user plane (U-plane) data forthe BS #2, the BS #3, and the BS #4, each being an SeNB as well as beinga second system, is transmitted to and received from the UE via one ofthe BS #2, the BS #3, and the BS #4, e.g., via the BS #2.

Specifically, the core network provides user plane (U-plane) data of thesecond system to a representative SeNB (BS #2). The representative SeNBthen provides the user plane (U-plane) data of the second system to theUE, and to the UE also via a plurality of SeNBs of the same system.

This can simplify processing of user plane (U-plane) data when a UEcommunicates with a plurality of base stations even in a case where anetwork that does not guarantee provisions of latency in data processingis employed between different communication systems.

Fourth Embodiment

In the conventional dual connectivity configuration, a UE notifies anMeNB of a measurement result of each base station as a measurementreport.

However, when a plurality of base stations form a communication systemas in the above first embodiment, notifying only the BS #1 ofmeasurement reports may cause processing concentration at the BS #1.

Particularly in the 5G system, the use of an array antenna havingdirectivity may attach beam characteristics to a transmission andreception signal, and therefore measurement information about beamcontrol etc. may be increased. Accordingly, measurement processing isrequired more times, in comparison with the conventional method.

In the present embodiment, in the configuration of the firstmodification of the first embodiment, a measurement result forconnection to the BS #2 is reported to the BS #1 before communicationbetween the BS #2 and the UE is established.

After communication between the BS #2 and the UE is established, the BS#1 is notified of a measurement report for the BS #1, and the BS #2 isnotified of measurement report for the BS #2, the BS #3, and the BS #4.

FIG. 32 is a diagram showing one example of a sequence of measurementreport processing of a communication system according to a fourthembodiment of the present invention.

When the UE is connected to the BS #1, in Step ST111, the UE notifiesthe BS #1 of measurement information about the BS #1 and the BS #2 asmeasurement reports.

In Step ST112, the BS #1 notifies the BS #2 of an addition request of abase station in order to determine whether communication between the BS#2 and the UE is possible based on the measurement information about theBS #2. Specifically, the BS #1 notifies the BS #2 of an addition requestof the BS #2.

In Step ST113, if the addition of a base station is possible, the BS #2notifies the BS #1 of an addition request acknowledge (hereinafter maybe referred to as an “addition request Ack”) as a positive response.

In Step ST114, the BS #1 notifies the UE of an RRC connectionreconfiguration message as an addition request of a base station.Specifically, the BS #1 notifies the UE of an addition request of the BS#2. The RRC connection reconfiguration message of Step ST114 may containinformation of a command to notify the BS #2 of measurement reports ofthe BS #2, the BS #3, and the BS #4.

In Step ST115, after completing establishment of communication with theBS #2, the UE notifies the BS #1 of an RRC connection reconfigurationcomplete message as an addition complete notification.

In Step ST116, after establishing communication with the BS #2, the UEnotifies the BS #1 of measurement information about the BS #1 as ameasurement report for the BS #1.

In Step ST117, the UE notifies the BS #2 of measurement informationabout the BS #2, the BS #3, and the BS #4 as a measurement report forthe BS #2.

In Step ST118, the BS #2 notifies the BS #3 of an addition request of abase station in order to determine whether communication between the BS#3 and the UE is possible based on the measurement information about theBS #3. Specifically, the BS #2 notifies the BS #3 of an addition requestof the BS #3.

In Step ST119, if the addition of a base station is possible, the BS #3notifies the BS #2 of an addition request Ack as a positive response.

In Step ST120, the BS #2 notifies the UE of an RRC connectionreconfiguration message as an addition request of a base station.Specifically the BS #2 notifies the UE of an addition request of the BS#3.

In Step ST121, after completing establishment of communication with theBS #3, the UE notifies the BS #2 of an RRC connection reconfigurationcomplete message as an addition complete notification.

In Step ST122, the BS #2 notifies the UE of measurement informationabout the BS #2, the BS #3, and the BS #4 as a measurement report.

In Step ST123, the BS #2 notifies the BS #4 of an addition request of abase station in order to determine whether communication between the BS#4 and the UE is possible based on the measurement information about theBS #4. Specifically, the BS #2 notifies the BS #3 of an addition requestof the BS #4.

In Step ST124 if the addition of a base station is possible, the BS #4notifies the BS #2 of an addition request Ack as a positive response.

In Step ST125, the BS #2 notifies the UE of an RRC connectionreconfiguration message as an addition request of a base station.Specifically, the BS #2 notifies the UE of an addition request of the BS#4.

In Step ST126, after completing establishment of communication with theBS #4, the UE notifies the BS #2 of an RRC connection reconfigurationcomplete message as an addition complete notification.

In Step ST127, after establishing communication with the BS #4, the UEnotifies the BS #1 of measurement information about the BS #1 as ameasurement report for the BS #1.

In Step ST128, the UE notifies the BS #2 of measurement informationabout the BS #2, the BS #3, and the BS #4 as a measurement report forthe BS #2.

Through the above processing, measurement information can be handled perradio system even if the radio system differs between the BS #1 ofLTE-A, for example, and the BS #2, the BS #3, and the BS #4 of 5G, forexample. Accordingly, a system can be constructed without affecting thesize of measurement information of other radio systems etc.

Further, the UE may be capable of selecting a base station used for thenotification of a measurement report. For example, the UE may use radioresources of the BS #3 and the BS #4 to notify of measurement reportsfor the BS #2, the BS #3, and the BS #4.

In this configuration, examples of a method of configuring the recipientof a measurement report include a method of using RRC messages. Withthis method, a measurement report can be notified of by using an idleradio resource even when pieces of measurement information are increaseddue to beam control etc.

If communication with a base station as the notification destination ofa measurement report is deleted, with the above-mentioned RRC messages,the notification destination of a measurement report may be changed ormay be returned to the notification destination before the change.

The embodiments and the modifications are merely illustrations of thepresent invention, and can be freely combined within the scope of thepresent invention. Any constituent elements of the embodiments and themodifications can be appropriately modified or omitted.

While the invention has been described in detail, the foregoingdescription is in all aspects illustrative and not restrictive. It istherefore understood that numerous modifications and variations can bedevised without departing from the scope of the invention.

EXPLANATION OF REFERENCE SIGNS

-   -   20 communication system, 21 first base station (MeNB), 22 second        base station (SeNB #1) 23 third base station (SeNB #2), 24 user        equipment (UE), 25 core network

The invention claimed is:
 1. A communication system comprising: acommunication terminal device; a plurality of base station devicesconfigured to perform radio communication with the communicationterminal device; and a core network configured to provide informationabout the communication with the communication terminal device to theplurality of base station devices, wherein the plurality of base stationdevices include a master base station device configured to perform mainprocessing, and a plurality of secondary base station devices to beconnected to the master base station device, at least one of controlplane data about control of the communication and user plane data abouta user is transmitted to and received from the communication terminaldevice via the master base station device, the control plane data andthe user plane data being contained in the information provided by thecore network about the communication with the communication terminaldevice, and one of the plurality of secondary base station devicesnotifies the communication terminal device of at least a part ofbroadcast information for at least another one of the plurality ofsecondary base station devices.
 2. The communication system according toclaim 1, wherein the core network provides the control plane data to themaster base station device, and the master base station device providesthe control plane data provided by the core network to the communicationterminal device, and also provides the control plane data provided bythe core network to the communication terminal device via the pluralityof secondary base station devices.
 3. The communication system accordingto claim 1, wherein the core network provides the user plane data to themaster base station device, and the master base station device providesthe user plane data provided by the core network to the communicationterminal device, and also provides the user plane data provided by thecore network to the communication terminal device via the plurality ofsecondary base station devices.
 4. The communication system according toclaim 1, wherein one of the plurality of secondary base station devicesperforms radio resource control processing on each of the plurality ofsecondary base station devices.
 5. The communication system according toclaim 1, wherein the one of the plurality of secondary base stationdevices notifies the communication terminal device of at least the partof broadcast information for each of the plurality of secondary basestation devices.